The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
In exploration drilling such as mineral exploration drilling, there is a need obtain representative samples for analysis to determine the geology of the earth formation being drilled.
The current practice when performing exploration drilling, such as mineral exploration drilling, is to send samples obtained during the course of drilling (e.g. core samples obtained from diamond drilling) to a laboratory (which is usually located remotely from the drilling site) for analysis to determine the geology of the earth formation that is being drilled. This usually results in a significant delay between the time that the samples are obtained and the time that the results of the analysis of the samples by the laboratory become available. The delay can be in the order of weeks or months. The delay in obtaining the analysis means that there is minimal, if any, feedback available for use in making decisions while drilling.
In an effort to reduce the aforementioned delay, there have been proposals to use drilling cuttings as a source of analysis to determine the geology of the earth formation that is being drilled. In this way, the drilling cuttings would constitute a continuous stream of sample material representative of the geological formation being drilled.
Typically in a drilling process, the drilling cuttings are conveyed to ground surface in a fluid, such as a drilling fluid (commonly referred to a drilling mud). The fluid can be captured and conveyed to a separation system at which at least some of the cuttings are removed. The removed cuttings can then be used for sampling. In one arrangement, all of the removed cuttings might be used for sampling; either as a continuous sample for analysis, or by being separated into batches providing individual samples for analysis. In another arrangement, only a portion of the removed cuttings are used for sampling; either as a continuous sample for analysis, or by being separated into batches providing individual samples for analysis.
The drilling fluid may form part of a fluid system, in which the drilling fluid is pumped down the drill string and returns upwardly along an annular space about the drill string, carrying the drilling cuttings. The returning fluid with the entrained drilling cuttings, is referred to herein as the drilling fluid returns.
The drilling fluid returns are captured in any appropriate way; for example, by collection at the upper end of a drill casing which extends into the borehole and along which the drill string passes, with the annular space around the drill string being defined between the drill string and the surrounding portion of the casing.
The fluid system may have a separation system at which at least some of the cuttings are removed from the drilling fluid returns. The separation system may separate the drilling cuttings in any appropriate way. The separation system may, for example, comprise a fluid flow path along which the drilling fluid returns can be conveyed, the fluid flow path incorporating a centrifuge for removal of cutting solids from the drilling fluid. The separation system may comprise part of a solids control system forming part of the fluid system. A solids control system likely to be particularly suitable is of the type disclosed in Australian Patent Applications 2012318265 and 2013204746, the contents of which are incorporated herein by way of reference.
There is need also to relate each sample to the axial location within the borehole at which the particular sample has been collected.
The samples may be taken incrementally by sampling in time intervals which represent specific spatial intervals of the borehole. By way of example, one or more samples may be taken at specific times, each specific time being related to the location within the borehole at which the drilling cuttings (providing the sample or samples) have been taken. In this manner, each sample is related generally to the location within the borehole at which the particular sample has been collected. The incremental samples can in collected and stored individually for subsequent analysis; for example, in sample collection bags.
In capturing the drilling fluid returns, it is desirable to collect the drilling fluid returns and convey the collected drilling fluid returns a continuous flow stream to a subsequent stage (at which drilling cuttings are to be removed from the drilling fluid). Collecting the drilling fluid returns and conveying the collected drilling fluid returns as a continuous flow stream serves to maintain the drilling cuttings in suspension within the drilling fluid. Maintaining the drilling cuttings in suspension within the drilling fluid is advantageous, as it may assist in avoiding blending of drill cuttings from different axial locations in the borehole, which would likely arise in circumstances where there was settling of the drill cuttings prior to removal from the drilling fluid. Blending of drill cuttings from different axial locations in the borehole may lead to samples which are less representative of the particular axial locations of the borehole to which discrete samples are attributed.
It is against this background that the present invention has been developed.
While the present invention has been developed against this background, it need not necessarily overcome any or all of the problems and difficulties referred to above. Rather, the invention may merely offer an alternative arrangement for facilitating the capture of drilling fluid returns in an exploration drilling process.